1. Field of the Invention
The present invention relates to a rechargeable battery, and more particularly, to a rechargeable battery including a bare cell having an electrode assembly, a battery can, a cap assembly and a protection circuit board electrically coupled to the bare cell.
2. Discussion of the Background
Rechargeable batteries are advantageous due to their compact size and high capacity. Types of rechargeable batteries nickel metal hydride (Ni—MH) batteries and lithium-ion batteries, such as Lithium-ion polymer batteries.
FIG. 1 is an exploded perspective view illustrating an example of a conventional can type lithium-ion battery. FIG. 2 is a partial perspective view showing a breaker and a lead plate installed on the cap plate of the bare cell before a protection circuit board is assembled with the bare cell.
Referring to FIG. 1 and FIG. 2, the lithium-ion battery may include a bare cell including an electrode assembly, an electrolyte, a battery can, and a cap assembly. The battery may also include a protection circuit board coupled to the bare cell to control voltages or currents during charging and discharging operations.
The electrode assembly 212 may be formed by stacking and winding a positive electrode 213, a separator 214, and a negative electrode 215 in a jelly roll shape. The positive electrode 213, separator 214, and negative electrode 215 may be thin films or plates.
The positive electrode plate 213 may include a positive charge collector made of a highly conductive metallic thin film, such as an aluminum foil, and a positive activation material layer coated on both sides of the positive charge collector. The positive activation material may include a lithium-based oxide material. A positive electrode tap 216 may be electrically coupled to a portion of the positive electrode 213 on which the positive activation material layer is not formed on the positive charge collector.
The negative electrode plate 215 may include a negative charge collector made of a highly conductive metallic thin film, such as a copper foil, and a negative activation material layer coated on both sides of the negative charge collector. The negative activation material may include a carbon-based material. A negative electrode tap 217 may be electrically coupled to a portion of the negative electrode 215 on which the negative activation material layer is not formed on the negative charge collector.
The polarities of the positive and negative electrode plates 213 and 215 may be switched, and polarities of the positive and negative electrode taps 216 and 217 may be also be switched. An insulation tape 218 may be wound around the positive and negative electrode taps 216 and 217 near the areas where the electrode taps 216 and 217 are extracted from the electrode assembly 212 to prevent a short circuit between the two electrodes 213 and 215.
The separator 214 may be made of polyethylene, polypropylene, or a co-polymer of polyethylene and polypropylene. The area of the separator 214 may be larger than the area of the positive and negative electrode plates 213 and 215 to prevent a short circuit between the two electrode plates 213 and 215.
The rectangular can 211 may be made of aluminum or an aluminum alloy and may have a hexahedral shape. The battery can 211 functions as a reservoir for storing the electrode assembly 212 and the electrolyte. The battery can 211 may serve as a terminal itself, or the cap plate of the cap assembly may serve as a positive electrode terminal.
The cap assembly may include a flat cap plate 110 that corresponds to the size and shape of the opening of the battery can 211. A terminal thru-hole 111 may be provided in the center of the cap plate 110. The electrode terminal may extend through the terminal thru-hole 111. A tubular gasket 120 may be arranged around the outer circumferential portion of the electrode terminal 130 between the electrode terminal 130 and the cap plate 110. An insulation plate 140 may be installed on the lower surface of the cap plate 110. The insulation plate 140 may have thru-holes corresponding to the center of the cap plate 110 and the terminal thru-hole 111 of the cap plate 110. A terminal plate 150 may be installed on the lower surface of the insulation plate 140.
The electrode terminal 130 may be inserted into the terminal thru-hole 11 of the cap plate 110. The lower end of the electrode terminal 130 may be electrically coupled to the terminal plate 150 with the insulation plate 140 being interposed between them.
The positive electrode tap 216 may be welded to the lower surface of the cap plate 110. The negative electrode tap 217 may be welded to the lower end of the electrode terminal 130. The negative electrode tap 217 may be folded into a serpentine shape.
An insulation case 190 may be arranged on top of the electrode assembly 212 to cover the top surface of the electrode assembly 212 and provide insulation between the electrode assembly 212 and the cap assembly. The insulation case 190 may be made of a polymer resin, such as polypropylene. A lead thru-hole 191 may be arranged on the insulation case 190 and the negative electrode tap 217 may extend through it. An electrolyte injection hole 192 may be arranged at another side of the insulation case 190. A lead thru-hole for the positive electrode tap 216 may be arranged next to the lead thru-hole 191 for the negative electrode tap 217 at the center of the insulation case 190.
An electrolyte injection hole 112 may be arranged at one side on the cap plate 110. The electrolyte injection hole 112 may be sealed with a plug 160 after the electrolyte is injected into the battery case. The plug 160 may include a ball type member made of aluminum or an aluminum alloy that is forcibly injected into the hole 112. The plug 160 may be welded to the cap plate around the electrolyte injection hole. The plug 160 may be made of a material similar to that of the cap plate 110 for a more robust weld.
The positions of the terminal thru-hole and the electrolyte injection hole of the cap plate, the holes through which the electrode tap is extracted from the electrode assembly, and the shape or the arrangement of the insulation plate or the terminal plate installed on the lower surface of the cap plate may be varied if the position of the electrode terminal is changed.
Contact portions between edges of the cap plate 110 and the side wall of the can 211 may be welded to combine the cap assembly with the can 211. The upper portion of the side wall of the can 211 may be bent inward to form a flange shape above the cap plate 110 after the cap assembly is assembled with the can 211.
A protrusion 310 may be arranged at one side of on the cap plate. The protrusion 310 may be engaged with a holder 320. The holder 320 may have inner diameter sized to fit snuggly onto the protrusion 310 to keep the holder 320 from moving if a horizontal force is applied. The holder 320 may be simply engaged with the protrusion 310, or may be welded to the protrusion 310 for a more robust engagement. If the holder 320 is welded to the protrusion 310, the holder 320 may made of a material similar to that of the protrusion 310.
The holder 320 may have an inner groove on its lower surface or may have an through hole, as shown in FIG. 1. A molding resin may be filled in the remaining space in the through hole to reinforce the holder 320. The holder 320 may be taller than the protrusion 310 to prevent a molding resin from slipping on the protrusion 310 and being separated from the unit cell 110 when a torsion stress is applied to the battery.
A separate conductive tap (not shown) may be installed on the terminal electrode 130 in a manner similar to the engagement between the protrusion 310 and the holder 320. The tap may be vulnerable to torsion stress because it is positioned in the center of the cap plate 110, but may serve as a support against a bending force.
The cap assembly may include a cap plate 110 covering the opening of the can 211, an electrode terminal 130 insulated from the cap plate 110 by a gasket 120, and a lead plate 410 for electrically coupling the bare cell to the protection circuit board 300. A breaker 420, which functions as a battery safety device, may also be included in the cap plate 110. The protection circuit board includes a pair of external terminals 311 and 312, as shown in FIG. 1 and FIG. 2, to connect the battery to a charger or other electronic devices.
One electrode of the electrode assembly 212 may be welded to the terminal plate 150 in the bare cell. The terminal plate 150 may be separated from the lower surface of the cap plate 110 by the insulation plate 140, and electrically coupled to the electrode terminal 130. The electrode terminal 130 may be insulated from the cap plate 110 by the gasket 120. The other electrode of the electrode assembly 212 may be directly welded to a surface of the cap plate 110.
The breaker 420 may be attached to an upper surface of the cap plate 110 and insulated from the cap plate 110 by a two-sided adhesive tape or an insulation tape 330. The electrode terminal 130 may be coupled to one electrical terminal 421 of the breaker 420. The other electrical terminal 423 of the breaker may be coupled to one electrical terminal 370 of the protection circuit board 300. A lead plate 410 may be welded to the cap plate 110 on the opposite side from the breaker 420 across the electrode terminal 130. The lead plate 410 may be coupled to the other electrical terminal 360 of the protection circuit board 300. The breaker 420 may be coupled in serial between the protection circuit board 300 and the electrode terminal 130 of the bare cell, so that a charging and discharging current may flows through the breaker. The breaker 420 may detect heat generated by an abnormality of the charging and discharging current and may shut down the current path.
The breaker 420 may include a bimetal switch. The bimetal switch may then close to resume the current flow when the temperature returns to normal. This type of protection circuit may be dangerous because although the current may be temporarily shut down due to an abnormal condition, the abnormal condition may not be eliminated and may resume when the current resumes so that the rechargeable battery may eventually explode. Positive temperature coefficient (PTC) elements may be used instead of conventional breakers because they cannot be closed again after opening due to an increase in temperature.
If a breaker 420 such as the one shown in FIG. 1 and FIG. 2 is used extra space for the breaker terminals 421 and 423 to couple the breaker 420 and the electrode terminal 130 and the breaker and the electrical terminal 370 of the protection circuit board will be required. The extra space required is counterproductive to the goal of producing a smaller rechargeable battery.
Additionally, an insulation tape or a two-sided adhesive tape 330 may be required to insulate the breaker from the cap plate. This increases the process and manufacturing costs.